Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$41.70	6.684%	$44.4872	$44.49	$44.50	$44.50
Purchase #2	$190.96	4.192%	$198.965	$198.97	$198.95	$199.00
Purchase #3	$53.63	10.307%	$59.1576	$59.16	$59.15	$59.20
Purchase #4	$131.75	3.723%	$136.6551	$136.66	$136.65	$136.70
Purchase #5	$18.32	5.141%	$19.2618	$19.26	$19.25	$19.30
Purchase #6	$80.76	11.301%	$89.8867	$89.89	$89.90	$89.90
Purchase #7	$52.33	4.446%	$54.6566	$54.66	$54.65	$54.70
7 purchase totals =	$569.45		$603.0700	$603.09	$603.05	$603.30